Studies on a dioxotetraamine macrocyclic ligand, its copper(II) and nickel(II) complexes and solution equilibria

Abstract

Reaction of diethyl 2-(4-nitrobenzyl)malonate with triethylenetetraamine yielded the macrocycle 12-(4-nitrobenzyl)-1,4,7,10-tetraazacyclotridecane-11,13-dione (L). Its complexes with Cu^II and Ni^II, i.e.[MH_–2L] and [ML]²⁺, were synthesised and characterized. Detailed studies have been made on the solution equilibria of L with five transition-metal and three rare-earth-metal ions. The stability of the transition-metal complexes accords with the Irving–William series and that of the rare-earth-metal complexes increases with decreasing metal-ion radii. The crystal structure of [H₂L][NO₃]₂·H₂O has been determined.